The rearrangement of 3-vinylcyclobutene derivatives promoted by metallic Lewis acids

The rearrangement of 3-vinylcyclobutene derivatives in the presence of metallic Lewis acids is discussed. Although most of the Lewis acids tried were too weak to cause any chemistry to occur, WCl6 and AlCl3 promote an interesting isomerization reaction. Especially significant is, for the first time, starting with a vinylcyclobutene, a product with a five-membered ring rather than a six-membered ring was obtained.